When nurturing aquarium fish in an aquarium, a filtration device is normally disposed to keep the water in the aquarium clean.
As a system for filtering water in an aquarium, for example, an external filtration system in which a filtration device is disposed separately from the aquarium, and an internal filtration system in which a filtration device is mounted in an aquarium are well-known.
For example, as shown in Patent Documents 1 and 2 listed below, in an internal filtration type aquarium system for aquarium fish, an inside of the aquarium is divided into a nurturing zone and a filtering zone. Furthermore, the filtering zone is divided into a plurality of water passage chambers which are in communication with each other, and various components, such as, e.g., a filtering material, a circulation pump, and a pipe, are accommodated in each water passage chamber.